如何更改标签栏项目的默认灰色? [英] How to change default grey color of tab bar items?

问题描述

我尝试更改 Tab Bar 项目的默认灰色，但 Xcode 发现错误.我使用了一些代码，该代码是:

I tried to change default grey color of Tab Bar items, but Xcode finds error. I used some code, that code is:

import UIKit

extension UIImage {
func makeImageWithColorAndSize(color: UIColor, size: CGSize) -> UIImage {
    UIGraphicsBeginImageContextWithOptions(size, false, 0)
    color.setFill()
    UIRectFill(CGRectMake(0, 0, size.width, size.height))
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image
  }
}

class SecondViewController: UIViewController {

let tabBar = UITabBar()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.



    UITabBar.appearance().selectionIndicatorImage = UIImage().makeImageWithColorAndSize(UIColor.blueColor(), size: CGSizeMake(tabBar.frame.width/CGFloat(tabBar.items!.count), tabBar.frame.height))

}

所以我把它放在 SecondViewController 中作为测试，当我在 Xcode Simulator 上运行应用程序时它崩溃并在日志中显示错误(控制台)致命错误:解包时意外发现 nil一个可选值

So I put this in SecondViewController just as test, and when I run application on Xcode Simulator it crash and it show error in logs (console) fatal error: unexpectedly found nil while unwrapping an Optional value

我认为问题出在这里:

    UITabBar.appearance().selectionIndicatorImage = UIImage().makeImageWithColorAndSize(UIColor.blueColor(), size: CGSizeMake(tabBar.frame.width/CGFloat(tabBar.items!.count), tabBar.frame.height))

因为当我删除这部分代码时，不会发生错误.有人可以帮我吗?

Because when I delete this part of code, error doesn't happen. Can someone help me ?

推荐答案

你创建 UITabBar 对象的代码中的问题，比如 let tabBar = UITabBar() 和这个对象与位于表单上的选项卡无关.你的 tabBar 是一个新的空对象，它不包含任何 UITabBarItem 对象，当你调用它时:

The problem in your code that you create UITabBar object like let tabBar = UITabBar() and this object has no relation to the tabs which are located on the form. Your tabBar is a new empty object that contains no one UITabBarItem objects and when you call this:

UITabBar.appearance().selectionIndicatorImage = UIImage().makeImageWithColorAndSize(UIColor.blueColor(), size: CGSizeMake(tabBar.frame.width/CGFloat(tabBar.items!.count), tabBar.frame.height))

当您尝试执行此操作时发生错误:tabBar.items!.count.您正在尝试解开可选的 items 数组 [UITabBarItem]? 并且它 nil 因为 tabBar 是空对象并且没有物品.

the error occurs when you try to do this: tabBar.items!.count. You're trying to unwrap optional items array [UITabBarItem]? and it nil becouse tabBar is empty object and have no items.

要解决此问题，您需要从当前 UITabBarController 获取对 UITabBar 的引用，例如:

To fix this you need to get reference to UITabBar from current UITabBarController for example like this:

class SecondViewController: UIViewController {

    var tabBar: UITabBar?

    override func viewDidLoad() {
        super.viewDidLoad()

        tabBar = self.tabBarController!.tabBar
        tabBar!.selectionIndicatorImage = UIImage().makeImageWithColorAndSize(UIColor.blueColor(), size: CGSizeMake(tabBar!.frame.width/CGFloat(tabBar!.items!.count), tabBar!.frame.height))
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

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